The invention relates to multilayer interference pigments having a blue mass tone.
Colored interference pigments are already known. They contain either colorant additives or coloring metal oxides, the latter possibly also forming the layer which produces interference colors. The play of colors brought about by this means is limited in nature. In particular, pigments with blue or bluish colors have not to date been obtainable in a satisfactory shade. The selection of desired colors is also restricted, in addition, because colorants may greatly reduce the chemical and thermostability of the interference pigments.
U.S. Pat. No. 3,951,679 describes colored pigments based on mica which is coated with metal oxide layers and may additionally carry a colored coating of Prussian Blue. The layer of Prussian Blue is formed by the reaction of an iron compound that has been deposited on the substrate with a water-soluble hexacyanoferrate. This pigment has the disadvantage that the Prussian Blue decomposes at a temperature of 200 to 300.degree. C.
U.S. Pat. No. 4,968,351 describes a pearl luster pigment which is colored by means of an adsorbed colorant, a color lake being applied to the colorant layer in order to intensify the adsorption of the colorant. A disadvantage of this pigment is that on contact with organic solvents the organic colorant is separated from the interference pigment. Moreover, the organic colorant impairs the weathering stability of the pigment. U.S. Pat. No. 5,169,442 describes a blue-green pigment consisting of a substrate comprising mica coated with metal oxide and of a top layer formed from a mixed oxide of magnesium oxide, calcium oxide, cobalt oxide and titanium dioxide. The mass tone of this pigment, however, is not pure blue.